Conventional high pressure transfer devices, such as shown in U.S. Pat. No. 4,082,368 (the disclosure of which is hereby incorporated by reference herein) provide for the effective high pressure feeding of a variety of liquid suspensions of particulate material, such as a slurry of wood chips, or a slurry of coal. While such structures are normally successful in performing their intended function, under some circumstances problems of clogging or excessively great wear of the housing-mounted screen associated with the device occur. It has been proposed (see Swedish Pat. No. 128,264 and copending application Ser. No. 123,947 filed Feb. 28, 1980) to mount the transfer device screen in the center of a pocket rather than in the rotor housing. While such a mounting of the screen avoids problems associated with the housing-mounted screen, it effectively reduces the volume of each pocket in half, minimizing the capacity of the transfer device.
According to the present invention, a high pressure transfer device and a method of conveying a liquid suspension of particulate material utilizing the transfer device are provided which have the aforementioned advantages associated with a center mounted screen, and minimize the above-mentioned disadvantage associated with such a screen.
The high pressure transfer device according to the present invention includes the conventional components of a pocketed rotor containing a pair of diametrically through-going pockets perpendicular to each other and rotatable about an axis, with a housing enclosing the rotor. The housing has four ports spaced around the periphery thereof for registry with inlets to and outlets from the through-going pockets. Means are provided for rotating the rotor in the housing with respect to the ports in a given direction of rotation, and a screen is disposed interiorly of each of the through-extending pockets between the inlet and outlet of each pocket. According to the invention, means are provided for mounting the screen within each pocket interior so that as liquid under pressure enters the pocket through the inlet thereof the screen will move to enlarge the volume between the inlet and the screen.
According to the invention, preferably the screen is formed as first and second screen portions, and a center component is disposed in each pocket (such as a center post coextensive with the axis of rotation of the rotor). The means for mounting the screen within the pocket comprises means for mounting each of the screen components with respect to the center component so that they are pivotal about an axis generally parallel to, or coextensive with, the rotor axis of rotation. Stop means are also provided for limiting the amount of pivotal movement of each screen portion of each screen about their axes so that the screen portions are never aligned with the pocket inlet or outlet. Thus each screen continues to effectively perform its screening function while providing an effective pocket volume almost as great as the pocket volume without a screen.
According to the method of the invention, a liquid suspension of particulate material may be continuously conveyed utilizing a high pressure transfer device as previously described. The liquid suspension that is conveyed may be a slurry of cellulosic particulate material suitable for the formation of paper pulp, or may be a slurry of hard particulate material, the particles having non-uniform and irregular shapes. Typical hard particulate materials that may be conveyed include undersea nodules (e.g. manganese nodules), coal, or rocks.
The method according to the invention comprises the following steps: (a) Continuously feeding liquid containing particulate material into a first of the housing ports for entry into a through-going pocket of the rotor. (b) Rotating the rotor in a given direction of rotation, so that it progressively rotates past each of the housing ports. (c) Providing withdrawal of liquid introduced through the first port from through-going pockets of the rotor through a third port of the housing, opposite the first port, and screening the particulate material above a predetermined size out of the liquid passing through the third port with the screen. (d) Pumping liquid under high pressure toward the rotor through a fourth port of the housing, the fourth port being located before the first port in the direction of rotation of the rotor, and between the first and third ports. (e) Providing withdrawal of liquid introduced through the fourth port, and entrained particulate material, through a second port located opposite the fourth port. And, (f) effecting adjustment of the volume of a pocket between the inlet to the pocket and the screen during introduction of liquid with entrained particulate material in step (a) to maximum effective pocket volume while not adversely affecting particulate material screening of step (c).
When constructing the rotor for the high pressure device according to the present invention, in view of the particular nature of the through-going pockets and the necessity for mounting the screens within the pockets, the rotor may be constructed in halves of solid material, with the pockets machined out of the halves. A metal plate is disposed between the rotor halves after insertion of the screens into the pockets, and end plates are disposed on the ends of the rotor, with the shaft for rotating the rotor extending through the interior of all the rotor components. The axis of rotation of the rotor may be horizontal or vertical, depending upon the particular use.
The invention also contemplates a rotor with particular center mounted screens for use in the high pressure transfer device.
It is the primary object of the present invention to provide a high pressure transfer device with a pocketed rotor having a center mounted screen which minimally restricts the effective volume of the rotor pockets, and a method of utilization of such a device for conveying a liquid suspension of particulate material. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.